1. Field of the Invention
This invention relates to a biometrics authentication method to perform individual authentication, biometrics authentication device, and blood vessel image reading device, which utilize characteristics of images of blood vessels which are a portion of a human body, and in particular relates to a biometrics authentication method, biometrics authentication device, and blood vessel image reading device, which are suitable for use in verifying registered blood vessel image information for a body against detected blood vessel image information for a body.
2. Description of the Related Art
There are numerous portions of the human body which can be used to differentiate the individual, such as fingerprints and toeprints, the retinas of the eyes, facial features, and blood vessels. With advances in biometrics technology in recent years, various devices have been provided which identify biometrics features of a portion of the human body to authenticate individuals.
Of these, blood vessels of the palms, backs of the hands and fingers provide a comparatively large quantity of individual characteristic data, and blood vessel (vein) patterns remain unchanged throughout life from infancy and are regarded as being completely unique, and so are well-suited to individual authentication. For example, in authentication technology of the prior art employing blood vessel images of the palm, at the time of registration or of authentication the user brings his palm into proximity with an image capture device. The image capture device emits near-infrared rays, which are incident on the palm of the hand. The image capture device uses a sensor to capture near-infrared rays rebounding from the palm of the hand.
Hemoglobin in the red corpuscles flowing in the veins has lost oxygen. This hemoglobin (reduced hemoglobin) absorbs near-infrared rays at wavelengths near 760 nanometers. Consequently when near-infrared rays are made incident on the palm of a hand, reflection is reduced only in the areas in which there are veins, and the intensity of the reflected near-infrared rays can be used to identify the positions of veins.
In order to utilize these blood vessel images for individual authentication, the user first uses an image capture device to register vein image data of the palm of his own hand in a server or on a card. Then, in order to perform individual authentication, the user employs an image capture device to cause the vein image data of his own hand to be read. The registered vein image retrieved using the ID of the user is verified against the vein pattern of the vein image for verification thus read, and based on the degree of similarity, individual authentication is performed (see Japanese Patent Laid-open No. 2000-293643).
With the widespread adoption of such biometrics authentication devices, it is anticipated that users will make use of the devices under various environmental conditions. For example, depending on the temperature, blood vessels (such as veins) in a human body may contract or expand. Because of this, in a cold state the veins (blood vessels) may contract, so that little blood vessel image information can be read, and verification errors tend to result.
Particularly when reading blood vessel images in the hand or fingers, because the hands and fingers are often exposed directly to the outside air, the temperature of the hands and fingers changes readily depending on the environment. For example, even when the biometrics authentication device is situated indoors in a temperature-controlled environment, if the user has entered the building from a cold outdoor environment, the hands and fingers may be at low temperature. If in this state biometrics authentication is attempted, little blood vessel image information can be read, as explained above, so that a verification error may occur.
Because the technology of the prior art does not assume that biometrics authentication will be performed in such an environment, so that contraction and expansion of blood vessels at the times of registration and verification is not taken into consideration, there is the possibility that verification may fail even when the individual in question is attempting authentication. Furthermore, it cannot be judged whether the cause of the verification failure is a difference in temperature, or the fact that the blood vessel image read is not that of the individual in question.
Consequently the widespread adoption of biometrics authentication equipment is impeded, and such verification failures cause the device to be perceived as unreliable by users; hence further innovations to make possible biometrics authentication in such environments are needed.